Coated sodium percarbonate granules with improved storage stability

ABSTRACT

The invention concerns coated sodium percarbonate granules comprising a core produced by fluidized bed spray granulation, containing sodium percarbonate as its main component, an inner coating layer containing an organic, hydrate-forming salt as its main component, and an outer coating layer containing as its main component at least one surfactant containing in the molecule one or more sulfate or sulfonate groups in the form of an alkali metal, alkaline-earth metal or ammonium salt. The invention also concerns a process for the production of the granules, the use of the granules in bleaching and cleaning agents, and bleaching and cleaning agents containing the granules. The sodium percarbonate granules according to the invention display improved storage stability combined with high internal stability and a high active oxygen content.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application represents U.S. national stage of internationalapplication PCT/EP2004/004355, which had an international filling dateof Apr. 24, 2004, and which was published in English under PCT Article21(2) on Nov. 18, 2004. The international application claims priority toEuropean application 03 010 225.5, filed on May 7, 2003.

FIELD OF THE INVENTION

The invention concerns coated sodium percarbonate granules with improvedstorage stability and a process for the production of these sodiumpercarbonate granules.

BACKGROUND OF THE INVENTION

Sodium percarbonate is used as a bleaching agent and as an activebleaching component in detergents and cleaning agents. The disadvantageof sodium percarbonate here is that it tends to decompose in contactwith moisture and with components of the detergent and cleaning agentcompositions, leading to a loss in active oxygen and hence in bleachingaction. In these applications sodium percarbonate is thereforepreferably used in the form of granules coated with a stabilisingcoating layer in order to achieve improved storage stability indetergents and cleaning agents.

It is known from EP-A 0 863 842 that sodium percarbonate granules withimproved storage stability can be produced by applying a firmly adheringcoating layer, consisting substantially of sodium sulfate, to a core ofsodium percarbonate produced by fluidised bed spray granulation.

WO 96/06801 describes coated sodium percarbonate granules havingimproved stability that are synthesised from a core of sodiumpercarbonate granules, an inner coating layer containing a sulfate orsilicate and an outer coating layer containing a compound (B) selectedfrom salts of monocarboxylic and dicarboxylic acids having 4 or morecarbon atoms and a compound (C) selected from salts of sulfated oils,α-olefin sulfonic acids and monoalkyl and dialkyl sulfosuccinates. Theexamples given in the specification show that the presence of compounds(B) is necessary to achieve an adequate storage stability and thatgranules containing only compound (C) and no compound (B) in the outerlayer display unsatisfactory storage stability.

JP-A 06-263434 describes stable in storage sodium percarbonate granulesthat are synthesised from surfactant-containing sodium percarbonategranules as the core, an inner coating layer consisting of a sulfate andan outer coating layer consisting of an anionic surfactant. Here thecore material is produced by crystallisation and subsequent granulationwith addition of the surfactant. From the examples and comparativeexamples given in the specification it follows that the core materialmust be produced with addition of a surfactant in order for the coatedsodium percarbonate obtained to display an adequate storage stabilityand that granules with a surfactant-free sodium percarbonate core, aninner coating layer consisting of a sulfate and an outer coating layerconsisting of an anionic surfactant display insufficient storagestability.

In the case of the sodium percarbonate granules described in EP-A 0 863842 there is still a need for an improvement in storage stability. Thesodium percarbonate granules described in WO 96/06801 have thedisadvantage that they are complicated to produce, since at least threedifferent compounds are necessary for coating the sodium percarbonategranules.

The sodium percarbonate granules described in JP-A 06-263434 have thedisadvantage that with the surfactant they contain an organic compoundin the sodium percarbonate core. This has a disadvantageous effect onthe internal stability of the sodium percarbonate granules and leads torestrictions in the storage of large amounts of the granules in silos.For storage in silos the sodium percarbonate granules must display highinternal stability, in other words low heat release during storage,since otherwise decomposition of the sodium percarbonate granules canoccur in the silo due to self-accelerating heating.

DESCRIPTION OF THE INVENTION

The object of the invention was therefore to provide coated sodiumpercarbonate granules having improved storage stability, which can beproduced by simple means and which combine the properties of highstorage stability in detergent and cleaning agent compositions and highinternal stability for storage in silos.

Surprisingly it was found that this object can be achieved by coatedsodium percarbonate granules comprising

-   a) a core produced by fluidised bed spray granulation, containing    sodium percarbonate as its main component,-   b) an inner coating layer containing an inorganic, hydrate-forming    salt as its main component and-   c) an outer coating layer containing as its main component at least    one surfactant containing in the molecule one or more sulfate or    sulfonate groups in the form of an alkali metal, alkaline-earth    metal or ammonium salt.

The invention also includes a process for the production of coatedsodium percarbonate granules with improved storage stability, comprisingthe following steps:

-   a) production of a core material by fluidised bed spray granulation,    wherein an aqueous hydrogen peroxide solution and an aqueous soda    solution are sprayed into a fluidised bed comprising sodium    percarbonate particles,-   b) application of an inner coating layer onto the core material from    step a) by spraying an aqueous solution in which at least one    hydrate-forming inorganic salt is dissolved and-   c) application of an outer coating layer onto the coated material    from step b) by spraying an aqueous mixture in which at least one    surfactant is dissolved or emulsified, which contains in the    molecule one or more sulfate or sulfonate groups in the form of an    alkali metal, alkaline-earth metal or ammonium salt.

The invention furthermore relates to the use of the sodium percarbonategranules according to the invention as bleaching agents or as activebleaching components in detergent and cleaning agents, and to bleachingagents and detergents and cleaning agents containing the sodiumpercarbonate granules according to the invention.

The sodium percarbonate granules according to the invention comprise acore produced by fluidised bed spray granulation, containing sodiumpercarbonate as its main component. Production of the core materialtakes place by known means by fluidised bed spray granulation, whereinan aqueous hydrogen peroxide solution and an aqueous sodium carbonatesolution are sprayed into a fluidised bed containing nuclei whosedimensions are smaller than the particles of the core material to beproduced and wherein water is evaporated at the same time. Sodiumpercarbonate is preferably used as the nucleus material. The corematerial is preferably produced by the method described in EP-A 0 716640.

The proportion of core material in the coated sodium percarbonategranules according to the invention is preferably in the range from 80to 99.5 wt. %, particularly preferably in the range from 90 to 99 wt. %and in particular in the range from 92 to 98 wt. %. The proportion ofsodium percarbonate in the core of the sodium percarbonate granulesaccording to the invention is preferably more than 80 wt. %,particularly preferably more than 95 wt. % and in particular more than98 wt. %. The proportion of organic carbon compounds in the core ispreferably less than 1 wt. %, particularly preferably less than 0.1 wt.% and in particular less than 0.01 wt. %.

In a preferred embodiment the core contains small amounts of additives,which have a stabilising effect on the active oxygen content, theproportion of stabilising additives in the core being preferably lessthan 2 wt. %. Magnesium salts, water glass, stannates, pyrophosphates,polyphosphates and chelating agents from the series comprisinghydroxycarboxylic acids, aminocarboxylic acids, aminophosphonic acids,phosphonocarboxylic acids and hydroxyphosphonic acids, as well as alkalimetal, ammonium or magnesium salts thereof, are preferably used asstability-increasing additives. In a particularly preferred embodimentthe core contains as stabilising additive an alkali metal silicate,preferably water glass, having a SiO₂/Na₂O modulus in the range from 1to 3, in a quantity from 0.1 to 1 wt. %. In the most preferredembodiment the core also contains in addition to this amount of alkalimetal silicate a magnesium compound in a quantity of 50 to 2000 ppmMg²⁺.

The coated sodium percarbonate granules according to the invention alsoinclude in addition to the core of sodium percarbonate an inner coatinglayer containing an inorganic, hydrate-forming salt as its maincomponent and an outer coating layer containing as its main component atleast one surfactant displaying in the molecule one or more sulfate orsulfonate groups in the form of an alkali metal, alkaline-earth metal orammonium salt. In addition to this inner and outer coating layer, thesodium percarbonate granules according to the invention can also containone or more additional coating layers, these being able to be positionedboth between the core and the inner coating layer and between the innerand the outer coating layer and outside the outer coating layer.

Between the coating layers and between the innermost coating layer andthe core there can be a clear boundary, at which the composition changesabruptly. Generally, however, a transition zone will form between theindividual coating layers and between the innermost coating layer andthe core, which contains the components from both adjoining layers. Suchtransition zones are formed for example by the application of a coatinglayer in the form of an aqueous solution, whereby as the layer starts toform, part of the layer beneath it is partially dissolved, such that atransition zone forms that contains the components of both layers. Inthis way, between the core and the inner coating layer a transitionlayer can form which contains sodium percarbonate, sodium carbonate,sodium hydrogen carbonate and the inorganic hydrate-forming salt fromthe inner coating layer. Similarly, between the inner coating layer andthe outer coating layer a transition layer can form which contains theinorganic hydrate-forming salt from the inner coating layer and thesurfactant from the outer coating layer.

The inner coating layer and outer coating layer are preferably formed insuch a way that they cover the underlying material by more than 95%,preferably more than 98% and in particular completely.

The inner coating layer of the coated sodium percarbonate granulesaccording to the invention contains an inorganic, hydrate-forming saltas its main component. The proportion of inner coating layer in thecoated sodium percarbonate granules according to the invention ispreferably in the range from 1 to 10 wt. %, particularly preferably inthe range from 2 to 7 wt. %. The proportion of inorganic,hydrate-forming salt in the material of the inner coating layer ispreferably at least 50 wt. %, particularly preferably at least 90 wt. %.The inorganic, hydrate-forming salt of the inner coating layer ispreferably chosen from the series comprising sodium sulfate, sodiumcarbonate, sodium hydrogen carbonate or magnesium sulfate. Mixtures andmixed salts of these compounds are also suitable. The inner coatinglayer particularly preferably contains sodium sulfate as the inorganichydrate-forming salt.

The outer coating layer of the coated sodium percarbonate granulesaccording to the invention contains as its main component at least onesurfactant containing in the molecule one or more sulfate or sulfonategroups in the form of an alkali metal, alkaline-earth metal or ammoniumsalt. The proportion of outer coating layer in the coated sodiumpercarbonate granules according to the invention is preferably in therange from 0.1 to 10 wt. %, particularly preferably 0.5 to 5 wt. % andin particular 1 to 3 wt. %. The proportion of surfactant in the materialof the outer coating layer is preferably at least 50 wt. % andparticularly preferably at least 80 wt. %. In a preferred embodiment theouter coating layer contains a mixture of surfactants, the surfactantmixture consisting of more than 50 wt. % of surfactants that contain inthe molecule one or more sulfate or sulfonate groups in the form of analkali metal, alkaline-earth metal or ammonium salt. The sulfate orsulfonate groups in the surfactant in the outer coating layer areparticularly preferably in the form of an alkali metal salt, mostpreferably in the form of the sodium salt.

In the outer coating layer alkyl benzene sulfonates, alkane sulfonates,α-olefin sulfonates, α-sulfo fatty acid esters or sulfosuccinates arepreferably used as surfactants having sulfonate groups. As alkyl benzenesulfonates, preferably those a straight-chain or branched alkyl groupwith preferably 8 to 20 carbon atoms, particularly 10 to 16 carbonatoms, are used. Preferred alkane sulfonates are examples havingstraight-chain alkyl chains with 12 to 18 carbon atoms. As α-olefinsulfonates, the reaction products from the sulfonation of α-olefinshaving 12 to 18 carbon atoms are preferably used. As α-sulfo fatty acidesters, sulfonation products of fatty acid esters produced from fattyacids having 12 to 18 carbon atoms and short-chain alcohols having 1 to3 carbon atoms are preferred.

Alkyl sulfates and ether sulfates are preferably used as surfactantshaving a sulfate group in the molecule. Preferred alkyl sulfates areexamples having straight-chain alkyl radicals with 12 to 18 carbonatoms. Preferred ether sulfates are the alkyl ether sulfates obtained byethoxylation of linear alcohols having 12 to 18 carbon atoms with 2 to 6ethylene oxide units, followed by sulfation.

In addition to the surfactants having sulfate or sulfonate groups, theouter coating layer can also contain other anionic surfactants as wellas non-ionic surfactants, cationic surfactants and amphotericsurfactants.

In a further embodiment of the invention, corresponding to DE 102 61161, the coated sodium percarbonate granules display an additionalcoating layer on top of the inner coating layer which contains as itsmain component an alkali metal silicate having a modulus of SiO₂ toalkali metal oxide of over 2.5. The additional coating layer can eitherbe between the inner and the outer coating layer or be positioned on topof the outer coating layer. The proportion of additional coating layerin the coated sodium percarbonate granules according to the invention ispreferably in the range from 0.2 to 3 wt. %. The proportion of alkalimetal silicate in the material of the additional coating layer ispreferably more than 50 wt. % and particularly preferably more than 80wt. %. Sodium water glass is preferably used as the alkali metalsilicate in the additional coating layer.

The sodium percarbonate granules according to the invention preferablydisplay an average particle diameter in the range from 0.3 to 2 mm,particularly preferably in the range from 0.5 to 1 mm. The sodiumpercarbonate granules according to the invention preferably contain onlya small proportion of fine particles. More than 90% of the particles inthe sodium percarbonate according to the invention preferably display adiameter of over 0.2 mm.

The invention also concerns a process for the production of coatedsodium percarbonate granules with improved storage stability, whichcomprises the following steps:

-   a) production of a core material by fluidised bed spray granulation,    wherein an aqueous hydrogen peroxide solution and an aqueous soda    solution are sprayed into a fluidised bed comprising sodium    percarbonate particles,-   b) application of an inner coating layer onto the core material from    step a) by spraying an aqueous solution, in which at least one    hydrate-forming, inorganic salt is dissolved and-   c) application of an outer coating layer onto the coated material    from step b) by spraying an aqueous mixture in which at least one    surfactant is dissolved or emulsified, which contains in the    molecule one or more sulfate or sulfonate groups in the form of an    alkali metal, alkaline-earth metal or ammonium salt.

Production of the core material from hydrogen peroxide and soda takesplace by known means by the fluidised bed spray granulation method andpreferably by the method described in EP-A 0 716 640. Here hydrogenperoxide and sodium carbonate solution are preferably reacted in a molarratio of H₂O₂ to Na₂CO₃ of 1.4 to 1.7, particularly preferably 1.5 to1.65. Hydrogen peroxide is used as an aqueous solution with preferably30 to 75 wt. % H₂O₂, particularly preferably 40 to 70 wt. % H₂O₂. Thehydrogen peroxide solution can additionally contain stabilisingadditives, such as e.g. complexing agents or magnesium compounds. Sodiumcarbonate is preferably used as an aqueous solution with a concentrationof between 10 wt. % sodium carbonate and the saturation concentration ofsodium carbonate, particularly preferably between 20 wt. % sodiumcarbonate and the saturation concentration of sodium carbonate. Thesodium carbonate solution can likewise contain stabilising additives,such as e.g. water glass. In the fluidised bed spray granulation processthe water introduced with the feed materials is evaporated and removedby feeding a drying gas into the fluidised bed. Air or a combustion gasobtained by burning a fuel such as e.g. natural gas with air ispreferably used as the drying gas. The drying gas is preferably suppliedto the fluidised bed at a temperature of between 120 and 400° C.,particularly preferably between 200 and 400° C. The temperature in thefluidised bed is preferably kept at between 40 and 95° C., particularlybetween 40 and 80° C. and in particular between 50 and 70° C.

In a preferred embodiment, nucleus material is supplied to the fluidisedbed in a quantity that leads to the formation of granules having anaverage particle size in the range from 0.2 to 2 mm. The core materialis preferably discharged from the fluidised bed by a classifyingprocess, and particularly preferably by the process described in EP-A 0938 922, such that preferably more than 90 wt. % of the core materialparticles discharged from the fluidised bed display a diameter of over0.2 mm.

The inner coating layer is applied by spraying an aqueous solution inwhich at least one hydrate-forming, inorganic salt is dissolved. Theinner coating layer is preferably applied by spraying an aqueous sodiumsulfate solution. The bulk of the water contained within the aqueoussolution is preferably evaporated by the input of heat as it is beingsprayed, such that during the application of the inner coating layeronly a small part of the core material begins to dissolve again and asolid coating layer is already formed from the hydrate-forming,inorganic salt during the spraying process. The inner coating layer ispreferably applied by spraying the aqueous solution of thehydrate-forming, inorganic salt in a fluidised bed and particularlypreferably by the process described in EP-A 0 970 917, with which adense coating layer can be achieved even with small amounts of coatinglayer material. Application of the inner coating layer in a fluidisedbed preferably takes place with the supply of a drying gas to thefluidised bed, such that a temperature in the range from 30 to 90° C. isestablished in the fluidised bed.

Application of the outer coating layer by the process according to theinvention is performed by spraying an aqueous mixture containing atleast one surfactant which contains in the molecule one or more sulfateor sulfonate groups in the form of an alkali metal, alkaline-earth orammonium salt, onto the granules coated with an inner coating layer. Theaforementioned alkyl benzene sulfonates, alkyl sulfonates, α-olefinsulfonates, sulfosuccinates, alkyl sulfates and ether sulfates arepreferably used as surfactants, either alone or in blends. Thesurfactants or surfactant blends can be sprayed both as aqueoussolutions and as aqueous emulsions. Solid surfactants that are poorlysoluble in water can be converted into sprayable aqueous emulsions byheating them above their melting point, by adding an auxiliarysurfactant, or by a combination of these two measures, in the presenceof water. During the application of the outer coating layer, the bulk ofthe water contained within the aqueous surfactant blend is preferablyevaporated by the input of heat as the aqueous blend is being sprayed,such that during the application of the outer coating layer only a smallpart of the inner coating layer begins to dissolve again and a solid orwaxy, surfactant-containing outer coating layer is formed as the outercoating layer is applied. The outer coating layer is preferably appliedby spraying the aqueous surfactant blend in a fluidised bed in which thematerial coated with the inner coating layer has been placed. The outercoating layer is particularly preferably applied by the processdescribed in EP-A 0 970 917, with which dense outer coating layers canbe achieved even with small amounts of surfactant. During application ofthe outer coating layer by spraying the aqueous surfactant blend in afluidised bed, a drying gas is preferably supplied to the fluidised bedsuch that a temperature in the range from 30 to 90° C. is established inthe fluidised bed.

In a preferred embodiment corresponding to WO 02/051745, the processaccording to the invention for producing coated sodium percarbonategranules includes an additional step of thermal aftertreatment at atemperature of 70 to 120° C., preferably 80 to 95° C., for a period ofat least 2 minutes, preferably 5 to 60 minutes, which is performed afterstep a), production of the core material by fluidised bed spraygranulation. The thermal aftertreatment is preferably performed afterstep b), application of an inner coating layer, and particularlypreferably after step c), application of the outer coating layer.

The invention also additionally provides the use of the coated sodiumpercarbonate granules according to the invention, or of the coatedsodium percarbonate granules produced by the process according to theinvention, as bleaching agents and as active bleaching components indetergents and cleaning agents.

The invention also provides bleaching agents having improved storagestability, which contain 15 to 99 wt. % of the coated sodiumpercarbonate granules according to the invention or of the sodiumpercarbonate granules produced by the process according to theinvention.

The invention likewise provides detergents and cleaning agents havingimproved storage stability, which contain 1 to 40 wt. % of the coatedsodium percarbonate granules according to the invention or of the coatedsodium percarbonate granules produced by the process according to theinvention.

The coated sodium percarbonate granules according to the invention andthe coated sodium percarbonate granules produced by the processaccording to the invention display improved storage stability indetergents and cleaning agents. In commercial, zeolite-containingdetergent blends, which are stored in commercial detergent packs, thecoated sodium percarbonate granules according to the invention displayan active oxygen loss of less than 20% when stored at 35° C. and 80%relative humidity for a period of 8 weeks, in other words the residualactive oxygen after storage for eight weeks is over 80% of the originalamount of active oxygen.

The coated sodium percarbonate granules according to the invention andthe coated sodium percarbonate granules produced by the processaccording to the invention also display a high internal stability, i.e.when stored in bulk they display only a low release of heat throughdecomposition reaction. After storage for 48 hours at 40° C. the amountof heat released by the coated sodium percarbonate granules according tothe invention, measured by the TAM method, is less than 5 μW/g andpreferably less than 3 μW/g. Determination of the heat release by theTAM method is performed by microcalorimetry using a thermal activitymonitor supplied by Thermometric AB, Järfälla (SE) over a 48 hourstorage period in a measuring cell at 40° C.

High storage stability combined with high internal stability can beachieved in the coated sodium percarbonate granules according to theinvention even with small quantities of coating agents and additives.The coated sodium percarbonate granules according to the invention thusdisplay a high content of sodium percarbonate and as a consequence ahigh active oxygen content. The active oxygen content, determined byredox titration of the hydrogen peroxide released after dissolving thegranules in water, is preferably more than 13.0 wt. % and isparticularly preferably at least 13.5 wt. %.

Coated sodium percarbonate granules according to the inventiondisplaying no other coating layers in addition to the inner and outercoating layer, exhibit short dissolving times when the granules aredissolved in water. For these sodium percarbonate granules coatedaccording to the invention the times to dissolve 95% of the granules inwater at 15° C., determined by conductometry, are less than 50% longerthan the times to dissolve non-coated sodium percarbonate corematerials.

By contrast, coated sodium percarbonate granules according to theinvention displaying an additional coating layer which contains as itsmain component an alkali metal silicate having a modulus of over 2.5,exhibit a delayed dissolution in water, with dissolving times ofpreferably more than 5 minutes, particularly preferably more than 10minutes. The granules having delayed dissolution display advantages whenused in detergents and cleaning agents containing oxidation-sensitiveenzymes. Through the delayed dissolution of the granules, the enzymescan act over a longer period of time before they are deactivated by thereleased active oxygen use.

EXAMPLES

-   a) Determining the dissolving time:    -   2 g of non-coated or coated sodium percarbonate are stirred into        1 l water at 15° C. The dissolving time is defined as the time        at which 95% is dissolved; this is determined by conductometry.        To compare the dissolving time of two differently        produced/coated products, they must display a comparable grain        size; if necessary, narrow screen fractions are compared with        one another.-   b) Determining the storage stability in detergent blends:    -   A phosphate-free but zeolite-containing detergent powder, TAED        activator and the coated sodium percarbonate are mixed together        in a quantity such that the mixture contains 5% TAED and the        active oxygen content is around 2.35 wt. %.    -   Components of the detergent powder in wt. %:

Anionic surfactants 12 Non-ionic surfactants 8 Zeolite A 36 Soda 10Sodium silicates 3 Remainder including moisture 31

-   -   800 g of each mixture are stored in commercial E1 detergent        packs, impregnated to be water-repellent and sealed, in a        conditioning cabinet at 35° C. and 80% relative humidity. The        active oxygen content is determined in the conventional way by        permanganometry. The retained active oxygen content is        determined as a percentage from the initial active oxygen        content and the active oxygen content after 8 weeks.

Comparative Example

Using the process described in EP-B 0 716 640, sodium percarbonategranules, having an average particle diameter of 0.75 mm and aproportion of fines under 0.2 mm of less than 2%, were produced from anaqueous hydrogen peroxide solution and an aqueous soda solution byfluidised bed spray granulation at a fluidised bed temperature of 50 to70° C.

The granules were coated with a sodium sulfate layer by the processdescribed in EP-B 0 863 842 in section [0021] by spraying a 20 wt. %sodium sulfate solution in a fluidised bed at a fluidised bedtemperature of 50 to 70° C. The amount of sodium sulfate solution waschosen such that 6 wt. % sodium sulfate, relative to the amount ofgranules used, was applied.

The sodium percarbonate granules coated with sodium sulfate displayed anactive oxygen content of 13.7 wt. %. In the TAM measurement the granulesdisplayed a release of heat of 2.2 μW/g after 48 hours at 40° C. Thedissolving time of the granules at 15° C. in water was determined as 1.5minutes.

After storage in a detergent blend for eight weeks at 35° C. and 80%relative humidity the residual content of active oxygen was 67% of theoriginal amount.

Example

1000 g of the sodium sulfate-coated sodium percarbonate granulesproduced in the comparative example were placed in a Strea-1 laboratorycoater supplied by Aeromatic and held in a fluidised bed with fluidisingair at 70° C. A 2 wt. % aqueous solution of sodium dodecyl benzenesulfonate (Lutensit A-LBN from BASF) was sprayed through a two-componentnozzle into the fluidised bed. The amount of surfactant solution waschosen such that 2 wt. % surfactant, relative to the amount of granulesused, was applied. Following spraying of the surfactant solution, thegranules were dried in the fluidised bed for a further 30 minutes at 70°C.

The sodium percarbonate granules coated according to the invention thatwere obtained had an active oxygen content of 13.6 wt. %. In the TAMmeasurement the granules displayed a release of heat of 2.1 μW/g after48 hours at 40° C. The dissolving time of the granules at 15° C. inwater was determined as 1.5 minutes.

After storage in a detergent blend for eight weeks at 35° C. and 80%relative humidity, the residual content of active oxygen was 88% of theoriginal amount.

1. A coated sodium percarbonate granule with improved storage stability,comprising: a) a core produced by fluidised bed spray granulationcomprising sodium percarbonate as its main component; b) an innercoating layer comprising an inorganic hydrate-forming salt as its maincomponent; and c) an outer coating layer comprising as its maincomponent at least one surfactant, wherein said surfactant comprises oneor more sulfate or sulfonate groups in the form of an alkali metal,alkaline-earth metal or ammonium salt.
 2. The sodium percarbonategranule of claim 1, wherein said core comprises 80-99.5 wt % of saidgranule.
 3. The sodium percarbonate granule of claim 1, wherein saidsodium percarbonate comprises greater than 80% of the weight of saidcore.
 4. The sodium percarbonate granule of claim 1, wherein organiccarbon compounds comprise less than 1 wt % of said core.
 5. The sodiumpercarbonate granule of claim 1, wherein said core further comprises 0.1to 1 wt % of an alkali metal silicate.
 6. The sodium percarbonategranule of claim 1, wherein said core comprises 50-2000 ppm Mg²⁺.
 7. Thesodium percarbonate granule of claim 1, wherein said inner coating layercomprises 1 to 10 wt % of said granule.
 8. The sodium percarbonategranule of claim 1, wherein said inorganic, hydrate-forming saltcomprises at least 50 wt % of said inner coating layer.
 9. The sodiumpercarbonate granule of claim 1, wherein said inorganic, hydrate-formingsalt in said inner coating layer is selected from the group consistingof: sodium sulfate; sodium carbonate; sodium hydrogen carbonate;magnesium sulfate; and mixtures or mixed salts of these compounds. 10.The sodium percarbonate granule of claim 9, wherein said inorganic,hydrate-forming salt is sodium sulfate.
 11. The sodium percarbonategranule of claim 1, wherein said outer coating layer comprises 0.1-10wt. % of said granule.
 12. The sodium percarbonate granule of claim 1,wherein said surfactant comprises at least 50 wt % of said outer coatinglayer.
 13. The sodium percarbonate granule of claim 12, wherein saidouter coating layer comprises a blend of surfactants and wherein atleast 50% of said surfactants in said blend comprise one or more sulfateor sulfonate groups in the form of an alkali metal, alkaline metal orammonium salt.
 14. The sodium percarbonate granule of claim 1, whereinsaid sulfate or sulfonate groups in said surfactant are in the form of asodium salt.
 15. The sodium percarbonate granule of claim 1, furthercomprising an additional coating layer, wherein said additional coatinglayer covers said inner coating layer and comprises, as its maincomponent, an alkali metal silicate having a modulus of SiO₂ to alkalimetal oxide of over 2.5.
 16. The sodium percarbonate granule of claim15, wherein said additional coating layer comprises 0.2-3 wt % of saidgranule.
 17. A composition comprising sodium percarbonate granulesaccording to claim 1, wherein the average particle size d₅₀ is in therange of 0.3 to 2 mm.
 18. A composition comprising sodium percarbonategranules according to claim 1, wherein more than 90 wt % of saidgranules have a diameter of more than 0.2 mm.
 19. A process for theproduction of coated sodium percarbonate granules with improved storagestability, comprising: a) producing a core by fluidised bed spraygranulation, wherein an aqueous hydrogen peroxide solution and anaqueous soda solution are sprayed into a fluidised bed comprising sodiumpercarbonate particles; b) applying an inner coating layer onto the coreof step a) by spraying an aqueous solution in which at least onehydrate-forming inorganic salt is dissolved; and c) applying an outercoating layer onto the coated core of step b) by spraying an aqueousmixture in which at least one surfactant is dissolved or emulsified andwherein said surfactant comprises one or more sulfate or sulfonategroups in the form of an alkali metal, alkaline-earth metal or ammoniumsalt.
 20. The process of claim 19, wherein said hydrate-forminginorganic salt in step b) is sodium sulfate.
 21. The process of claim19, wherein said inner coating layer and said outer coating layer areapplied by spraying in a fluidised bed.
 22. The process of claim 21,wherein said inner coating layer and said outer coating layer areapplied at a temperature in the range of 30-90° C.
 23. A composition forbleaching or cleaning, wherein said composition comprises sodiumpercarbonate granules according to claim
 1. 24. The composition of claim23, wherein said composition is a bleaching agent and comprises 15-99 wt% of said sodium percarbonate granules.
 25. The composition of claim 22,wherein said composition is a detergent or cleaning agent and comprises1-40 wt % of said sodium percarbonate granules.